The present invention relates to a method of and a roll stand for diagonal rolling of tubes.
Various methods are known for diagonal rolling of tubes or tube ingots. Such diagonal rolling processes are performed for example on rolling devices identified as diagonal rolling mechanism, assel rolling mill, diescher rolling mill, planetary skew rolling mill, cone skew rolling mill, etc. When such devices are utilized for rolling medium or thin-walled rolling ingots, or in other words such which have a diameter/wall thickness ratio of approximately greater than 10:1, problems arise during rolling of the rear rolling ingot ends as considered in the rolling direction. During the rolling process they expand in a funnel-shaped manner in a radial direction, which leads to rolling errors and to jamming of the tube ingot ends in the caliber opening of the roll stand. The reason for this disadvantageous expansion is that during the progressing rolling process the support of the rolling ingot wall against the expansion due to the not yet rolled and therefore still thick-walled rear part of the rolling ingot progressively reduces and finally disappears.
For avoiding such an expansion of the tube ingot ends, it was proposed in the German patent document DE-PS 38 23 135 to reduce the outer diameter and/or the wall thickness of the tube ingot end before it is inserted in the caliber opening of the diagonal roll stand. In this known process an additional working step must be performed with respect to the rolling ingot ends and an additional device is needed which is suitable for reducing the tube ingot ends before the diagonal rolling itself.
Contrary to this, in accordance with the solution proposed in the German document DE-OS 15 27 750 the tube ingot ends are provided with a greater wall thickness. This is obtained in that during the diagonal rolling the rolls are displaced from one another in a radial direction when the tube ingot ends come into proximity to the rolls. The adjustment of the rolls required for this must be performed however precisely, which includes substantial difficulties and high expenses. This means that in addition to the rolls, also extensive bearing inserts and guiding elements or in other words many parts must be also adjusted synchronously and with a high accuracy to maintain the required roll tolerances. This involves further difficulties that the parts to be displaced have high weight and they are loaded during adjustment with great working forces, since the adjustment must be performed during the rolling. Moreover, it is necessary to perform the adjustment fast, so that the tube ingot ends with a thickened wall are maintained as brief as possible, which involves a substantial loss since later they are separated and must be scrubbed. Furthermore, the known processes cannot be utilized with planetary diagonal roll stands since there the rolls are supporting in a rotor which rotates with a high speed and therefore fast radial adjustment of the rolls during the rolling process is not possible.